GB2273784A

GB2273784A - A method and system for detecting the travel position of a body

Info

Publication number: GB2273784A
Application number: GB9326145A
Authority: GB
Inventors: Frank Kursawe; Horst Fuhrmann; Ralf Noltemeyer; Wolfgang Welsch
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1992-12-24
Filing date: 1993-12-22
Publication date: 1994-06-29
Also published as: JPH06241261A; GB9326145D0; DE4244078A1

Description

2273784

DESCRIPTION A METHOD AND SYSTEM FOR DETECTING THE TRAVEL POSITION OF A BODY

The invention relates to a method and system for detecting the position of a first body with respect to a second body of a device, such as a vehicle shock absorber, having two bodies movable relative to one another.

In a method and system known, for example. from DE-A- 40 29 633, which describes a sensor integrated with a vehicle shock absorber for measuring the defluction of the vehicle suspension springs, the inductance of a measuring coil is influenced with the aid of a material which can be magnetised or of a highly electrically conductive material, in dependence upon the travel position, either directly magnetically or indirectly in accordance with the eddy current principle, in such a way that a continuously variable sensor output signal is produced along the travel path.

In the known system the sensor elementis connected to the evaluating electronics in the sensor housing of the running gear control device by means of a cable harness. Since the sensor elements in this embodiment cannot be alignedr greater tolerances can arise with regard to the effect of temperature. the -2zero point displacement (Offset) and the sensitivity or amplification.

It is an object of the invention on the basis of the known process or travel measuring system to provide a new method or travel measuring system in which tolerances of parameters influencing the precision of the measuring results can be reduced to a minimum.

One aspect of the invention is a method of detecting the travel position of a first body with respect to a second body of a device having two bodies movable relative to each other along a travel path in which measuring device a continuously variable position signal corresponding to the travel position of the first body along the travel path is produced by means of a measuring device and in which a marking signal is produced for at least one defined travel position of the first body by additional means.

According to another aspect of the invention, a travel measuring system for detecting the travel position of a first body with respect to a second body of a device having two bodies movable relative to each other along a travel path, comprising a measuring device for producing a continuously variable position signal corresponding to the travel position of the first body along the travel path, and additional means -3for producing a marking signal for at least one defined travel position of the first body.

The important advantage arises that. on the one hand, the high sensitivity of the known continuous travel measuring technique can be fully utilised and, on the other hand, with the aid of marking signals for at least one defined travel position. at least one parameter, influencing the measuring result, can be corrected during the running operation.

The basic principle of the process and travel measuring system in accordance with the invention is thus to be seen in the fact that an extremely sensitive continuous fine measuring technique, with time and temperature dependent parameters, overlies to a certain extent a course measuring technique for one or a small number of travel positions, in order in this way when passing through one or a small number of positions of the travel path. to obtain additional information about the instantaneous values of one or several parameters, and then to correct these parameters correspondingly, in order to reduce the measuring errors to a minimum, and in fact not only at the predetermined travel position or at the predetermined travel positions but continuously for the entire measuring pathr which path can be equal to the travel path or can comprise one or several regions -4which are interesting with respect to the measuring technique.

In principle, a marking signal for one or several travel positions can be obtained by means of switching devices working mechanically or in a contact free manner, the elements of which switching devices are provided at defined positions of the bodies which move relative to each other, wherein it is particularly advantageous to choose the position of a least one travel position in such a manner that, in practice during a measuring process, the travel position can.be passed through in each case once after an extremely short time; for example the neutral position of the bodies, which are movable relative to each other, can be chosen as the travel position for the purpose of a predetermined application purpose.

In one embodiment of the invention it is particularly advantageous, when the additional devices comprise a material influencing the inductance andlor the working resistance of a measuring coil in at least one defined travel position of the first body, in such a way that. when this travel position is passed by the first body, a pulsed marking signal is produced by the measuring coil. Thus the material can. in an advantageous manner, be a magnetically active material, in particular a material that is highly -5permeable, which material directly influences the inductance and/or the effective resistance of the measuring coil, or also a highly electrically conductive material, whilst, during the supply of the measuring coil with an alternating current, eddy currents can be produced, which eddy currents in dependence upon frequency indirectly.influence the inductance and/or the effective resistance of the measuring coil.

A travel measuring system has proved to be particularly advantageous in which system the material influencing the inductance and/or the effective resistance of the measuring coil is a highly electrically conductive material and in which the measuring coil is supplied, for the production of eddy currents in this material. with an alternating voltage or an alternating current of a predetermined frequency. In this embodiment which renders possible the production of a measuring signal which is continuously variable along the travel path. the additional devices can be preferably formed in such a way that they comprise an alternating current source to supply the measuring coil with a second alternating voltage or a second alternating current, the frequency of which is markedly lower that the predetermined frequency for the first alternating voltage. A larger -6radial penetration depth of the eddy currents in the highly electrically conductive material is thereby achieved, wherein then, when in this material at least one discontinuity is provided, which corresponds to a predetermined travel position, upon the passing of the discontinuity a pulsed marking signal can be produced by the measuring coil by reason of the alternating current of a lower frequency flowing through the measuring coil.

The invention is further described, by way of example, with reference to the accompanying drawings, in which:- Fig. 1 is a longitudinal sectional view through a single-tube shock absorber having a travel measuring system in accordance with the invention; Fig. 2 is a graph to explain the course of a continuously variable position signal with respect to the travel path; Fig. 3 is a graph of the course of an additional signal having individual marking signals over the travel path; and Fig. 4 is a schematic illustration to explain a constructive variation for the production of marking signals.

Fig. 1 illustrates a single-tube shock absorber 2, wherein a middle piece, not of interest here, of -7this shock absorber 2 is omitted in order to be able to show the remaining parts on a larger scale. The shock absorber 2 comprises essentially a cylinder 4 having a wall 5, a first or upper end 6 and having a second or lower end 8, as well as a damping piston 10 and a piston rod 12. The damping piston 10 is mounted inside the cylinder 4 in an axially displaceable manner along an inner peripheral surface 14 of the wall 5. The piston rod 12 is connected by one end to the damping piston 10 and protrudes by its other end through the upper end 6 beyond the cylinder 4. A seal 15 provided at the upper end 6 seals a leakage gap between the upper end 6 and the piston rod 12. The end of the piston rod 12 protruding beyond the cylinder 4 in an axial direction is connected to a first mass 16. The lower end 8 of the cylinder 4 is articulated to a second mass 18. The first mass 16 is, for example, a motor vehicle body and the second mass 18 is, for example, a motor vehicle axle. An inner chamber of the cylinder 4 is divided by the damping piston 10 into a first working chamber 21 and a second working chamber 22. The first working chamber 21 is situated on the side of the damping piston 10 facing the upper end 6 and the second working chamber 2 is situated on the side of the damping piston 10 facing the lower end 8. In the -8drawing the first working chamber 21.is situated above and the second working chamber 22 below the damping piston 10. For the purpose of compensating for the differences in volume when the piston rod 12 is travelling in and out, the second working chamber 22, for example, can be connected to an accumulator 24. Both the working chambers 21, 22 and the accumulator 24 are at least partially filled with a pressure medium.

The two working chambers 21, 22 are connected to each other by means of at least one flow connection 26. An electrically controlled solenoid valve 28, for example, can be provided in the flow connection 26. It is possible by means of the solenoid valve 28 to influence the commencement of a throttling operation of the pressure medium upon the pressure medium flowing through the flow connection 26. The solenoid valve 28 is connected by means of a line 32 to electronics 30, provided in the first mass 16, and can be controlled by the electronics 30. In addition to the flow connection 26, additional flow connections 34 can be provided to interconnect the two working chambers 21, 22. Non-return valves 35. for example, can be provided inside the additional flow connections 34. The flow connection 26 and the additional flow connections 34 are disposed in the illustrated -9embodiment inside the damping piston 10.

An annular groove 38 is provided in outer periphery 36 of the damping piston 10. A measuring coil 40 is situated inside the annular groove 38. The measuring coil 40 comprises at least a coil 42 and preferably also a core 44. The core 44 consists. for example, of a soft magnetic, highly permeable material and largely surrounds the coil 42. however it leaves the coil 42 free at an outer surface facing the wall 5. The coil 42 consists chiefly of a wire which is insulated, wound in multi-layers and electrically conductive. The coil 42 is likewise connected to the electronics 30 by means of a line 32. The core 44 markedly improves the operation of the measuring coil 40.

In addition to the measuring coil 40 or instead of the measuring coil 40 another measuring coil 46 or a measuring coil 48 can be provided. The measuring coil 46 is disposed on the damping piston 10 at the front end facing the first working chamber 21 and the other measuring coil 48 is disposed on the side of the damping piston 10 facing the second working chamber 22. The measuring coils 46, 48 each comprise likewise a coil 42 and a core 44. For the travel measuring system. in accordance with the invention, a coil 42 and therewith one of the measuring coils 40, 46, 48 is -10sufficient in principle, and depending upon the conditions only one of the measuring coils 40 or 46 or 48 is disposed as favourably as possible. Explanations relating to the measuring coil 40 also apply to the other measuring coils 46, 48.

The wall 5 of the cylinder 4 has an outer peripheral surface 54. A material 60, influencing the inductance of the coil 42, is disposed on the outer peripheral surface 54 of the cylinder 4.

The material 60 influencing the inductance can have, for example, as shown in DE-A- 40 29 633, Fig. 2, a recess 68 formed in an axial direction in the shape of a V, in order to render possible the production of a continuously variable position signal, as shown in Fig 2. Other possibilities for the form of the material or the material layer 60 for the achievement of this aim are described in the cited printed document.

The measuring coil 40 is in an axial direction, ie, in a direction towards the travel path running parallel to the longitudinal axis of the shock absorber 2, considerably shorter than the maximal permissible travel path. On the other hand, the material influencing the inductance extends at least over the entire length of the measuring path. In the illustrated embodiment the material 60 surrounds the -11measuring coil in the region of the first end 6 has a larger angle than in the region of the second end 8.

Depending upon the travel position of the measuring coil 40 or of the coil 42 with respect to the cylinder 4, the influence of the material 60 is as a result greater or smaller. Furthermore, the influence of the material 60 on the inductance and, if necessary, on the effective resistance of the measuring coil 40 or of the coil 42 is a measure for the travel position of the measuring coil 40 along the travel path or with regard to the cylinder 4.

In the illustrated embodiment, the material influencing the inductance and/or the effective resistance having its special structure, previously explained, or a geometric form, is a highly electrically conductive material, which is as nonmagnetic as possible, for example copper or aluminium. On the other hand. the wall 5 consists, at least along the travel path. preferably of non-magnetic material which is a poor conductor of electricity, for example of a suitable high-alloy steel. In this case, the inductance of the measuring coil 40 or of the coil 42 is relatively large when it is situated in the region of the second end 8, since in the region of the recess 68, which is relatively wide at this point, no eddy currents are produced, which by reason of their -12feedback to the measuring coil could reduce the inductance andlor the effective resistance of the measuring coil. In contrast, in the region of the first end 6, the inductance of the measuring coil 40 or of the coil 42 is relatively small, since at this point eddy currents in the material 60 are produced practically over the entire outer surface of the measuring coil. Since the width of the recess 68 is continuously altering along the travel path the possibility exists of detecting any travel position whatsoever with the aid of the ascertained inductance of the measuring coil. Thus a continuously variable position signal, in accordance with Fig 2, can be obtained along the travel path and more precisely in dependence upon the supplying of the measuring coil 40 or of the coil 42 with an alternating current having a predetermined frequency fl.

The structured material 60 is surrounded, in accordance with Fig.1, by a cover tube 80 in which recesses 82 are provided at predetermined intervals along the travel path. When the measuring coil 40 is then additionally supplied with an alternating current, the frequency f2 of which is markedly lower than the frequency fl, so that a larger penetration depth arises outwards in a radial direction. for the magnetic alternating field produced by the coil 40, -13then the inductance of the measuring coil changes suddenly for this second frequency f2, when upon passing through the travel path one of the recesses 82 of the cover tube 80. made of highly electrically conductive material, is passed. Sudden changes in the coil inductance and/or of the effective resistance of the same thus arise, which changes are superimposed on the continuous change in these parameters of the coil in dependence upon the material 60. In addition to the continuous "fine signaP, f, in accordance with Fig. 2, a "coarse signaP, g is obtained as shown in Fig. 3. This signal can be prepared with the aid of the electronics 30 in such a way that defined marking signals or pulses M. as shown in the lower part of Fig. 3, arise along the travel path for defined travel positions. the position of which travel positions correspond to the position of the recesses 82 of the cover tube 80. Corresponding results are obtained when recesses 821 are provided in the structured material 60 itself at suitable positions, as shown in the schematic sketch in accordance with Fig. 4. In particular when the markings or recesses are provided directly in the magnetically active material, the cover tube can if the case arises be omitted.

In the embodimentAllustrated in Figs. 1 and 4, the measuring coil 40 obtains or generates its -14continuously variable position signal, by being movable along a material 60 influencing the inductance and/or effective resistance of the measuring coil 40 and having a structure. A measuring signal obtained in the measuring coil 40 in each case according to the position of the measuring coil 40 relative to the structural material 60.

An excitation coil can be used in place of the structured material 60, the excitation coil being fed for example with an electrical alternating voltage. A continuously variable position signal is obtained in the measuring coil 40 in each case according to the position of the measuring coil 40 relative to the excitation coil. This signal varies analogously according to the movement of the measuring coil 40 relative to the excitation coil. In this variant, the additional device can also be provided which generates for at least are predefined position of the two bodies relative to one another, a pulse-like marking signal when this predefined relative position is passed.

Thus, in the method, in accordance with the invention, the possibility exists to produce simultaneously a fine signal, in accordance with Fig. 2, . and a coarse signal, in accordance with Fig. 3, upon passage along the travel path, wherein the coarse signal serves to scale the fine signal which -is- signal serves to scale the fine signal which continuously changes along the travel path. In particular it is already possible when detecting a single marking signal M. in accordance with the invention, to recognise and correct a zero point displacement of the fine signal. As soon as, in the course of a measuring process, a further marking signal M is detected the possibility exists to adjust, in addition, the sensitivity of the sensor system with regard to the fine signal and, to a certain degree, to correct the ascending gradient of the straight lines schematically illustrating the fine signal in Fig. 2. As a result. the sensitivity and the zero-point displacement for the fine signal can thus be detected in dependence upon the detection of two marking signals and can be corrected corresponding to the respective requirements, which is achieved preferably with the aid of a micro-processor, which microprocessor calculates the required adjustment values from the measured values, stores the adjustment values in the associated memory devices and. if required, updates them. so that - if necessary, apart from a short start- up phase - corrected measuring values are available, which are extremely precise and consequently render possible the production of extremely precise control signals, for example, for the solenoid valve -1628.

The signal-voltage curves f and g, illustrated in Figs. 2 and 3, over the travel path are merely to be qualitatively understood, wherein the evaluating switching, as mentioned, favours a micro processor. arranged and programmed in such a manner, known to the person skilled in the art and therefore not requiring more detailed explanation here, that the curves desired for the purpose of obtaining and evaluating a signal can be achieved.

Finally, by a continuously variable position signal or a continuous measuring signal is understood to be a signal which is produced continuously along the entire measuring path or the sections of the same, wherein a digital signal in the sense of the existing application is also observed as a continuous signal, although a signal change can be achieved only in predetermined small steps differently to the case of the analogous signal.

Claims

-17CLAIMS

1.A Method of detecting the travel position of a first body with respect to a second body of a device having two bodies movable relative to each other along a travel path in which measuring device a continuously variable position signal corresponding to the travel position of the first body along the travel path is produced by means of a measuring device and in which a marking signal is produced for at least one defined travel position of the first body by additional means.

2. A travel measuring system for detecting the travel position of a first body with respect to a second body of a device having two bodies movable relative to each other along a travel path, comprising a measuring device for producing a continuously variable position signal corresponding to the travel position of the first body along the travel path, and additional means for producing a making signal for at least one defined travel position of the first body.

3. A travel measuring system according to claim 2, wherein the measuring device comprises a measuring coil on the first body and a material influencing the inductance of the measuring coil on the second body, which material along the travel path has a structure analogously connected to the travel position, and -18wherein the additional means comprise a material influencing the inductance andlor the effective resistance of the measuring coil in at least one defined travel position of the first body in such a way that, when this travel position is being passed by the first body. a pulsed marking signal can be produced by the measuring coil.

4. A travel measuring system according to claim 2, wherein the measuring device has two coils of which one coil is formed as an excitation coil supplied with an electric alternating voltage and is connected to a body, and of which coils the other is formed as a measuring coil and is connected to the other body in such a way that, by reason of the variable electromagnetic coupling of the same, in dependence upon the spacing between the two coils. the variable position signal can be produced. and wherein the additional means comprise a material influencing the inductance andlor the effective resistance of the measuring coil in at least one defined travel position of the first body in such a way that, when this travel position is passed by the first body a pulsed marking signal can be produced by the measuring coil.

5. A travel measuring system according to any of claims 2 to 4, in which the additional means are formed in such a way that, along the travel path, an -19effective signal can be produced for at least two defined travel positions of the first body respectively.

6. A travel measuring system according to claim 3, in which the material influencing the inductance and/or the working resistance of the measuring probe is a highly electrically conductive material and the measuring coil is supplied with an alternating current of predetermined frequency for the production of eddy currents in the highly electrically conductive material, and in which the additional means comprise an alternating current source to supply the measuring coil with a second alternating current, the frequency of which second current is markedly lower than the predetermined frequency of the first alternating current, in order to achieve a greater radial penetration depth into the highly electrically conductive material, and at least one discontinuity, corresponding to a predetermined travel position, is provided in the highly electrically conductive material in such a way that. when the discontinuity is passed by the first body, a pulsed marking signal can be produced by the measuring coil, by reason of the lower frequency of its applied alternating current.

7. A travel measuring system according to any of claims 2 to 6, in which evaluating devices are -20provided, with the aid of which the position signal produced by the measuring device can be altered, in dependence upon the occurrence of a marking signal, for the purpose of increasing the measuring accuracy.

8. A travel measuring system according to claim 7. in which the evaluating devices are formed in such a way that, by virtue thereof, a zero point displacement of the position signal can be corrected, in dependence upon a marking signal.

9. A travel measuring system according to claim 8, in which the evaluating devices are formed in such a way that. by virtue thereof, in dependence upon at least one further marking signal allocated to a different defined travel position, at least one further parameter of the position signal can be altered with the aim of improving the measuring accuracy.,

10. A travel measuring system according to claim 9, in which the evaluating devices are formed in such a way that. by virtue thereof, in dependence upon two marking signals which are allocated to two defined travel positions, the zero point displacement of the position signal and the sensitivity of the measuring device can be corrected.

11. A travel measuring system according to any of claims 7 to 9, in which calculating and memory -21devices are provided, with the aid of which, in dependence upon at least one marking signal, at least one correction value for the position signal or for the measuring device can be calculated and stored.

12. A method of detecting the travel position of a first body with respect to a second body, substantially as herein described with reference to the accompanying drawings.

13. A travel measuring system, constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.